Information is stored in concentric tracks on opposite sides of a data storage disk. The information is accessed by a combination of movement of a read/write head to a particular track and rotation of the disk to the segment of the track that contains the desired information. Track seeking may be executed by linear actuation in which the read/write heads are moved radially along the opposite sides of the data storage disk or may be implemented mented using rotary actuation in which the read/write heads are mounted to an arm assembly that is pivoted at an end that is opposite to the heads.
Disk rotation is achieved by a disk drive assembly that conventionally includes a stationary shaft and a rotating sleeve to which the data disk or a stack of data disks is coupled. The sleeve is motor driven to precisely cisely position a track segment relative to a read/write head. As the density of data on the disks increases, the requirement of precise positioning is also increased. Consequently, spindle bearings for disk drive assemblies have received increasing attention. Spindle bearings must accommodate both the radial loads and the axial loads of a disk drive in which rapid accelerations and decelerations are critical.
The conventional approach to providing bearings for a disk drive assembly is to utilize ball bearings. However, such contact bearings are associated with a number of concerns. Perhaps least importantly, the contact bearings generate noise which is audible at the exterior of the host computer. More importantly, for the long-term perspective, the ball bearings wear and may eventually cause failure of the disk drive assembly. The wear also generates particles which may migrate to a data disk and cause the loss of data. From a shorter term perspective, there are limitations to the precision of operation of the contact bearings. For example, contact bearings experience non-repetitive runout, i.e., a slight but unpredictable shifting of the center of rotation as a result of solid surfaces interacting in a semi-random fashion. Non-repetitive runout is primarily a radial uncertainty, but also causes some axial variability.
An alternative approach is to use hydrodynamic bearings within a disk drive assembly. U.S. Pat. No. 5,112,142 to Titcomb et al. describes a bearing assembly to provide hydrodynamic support for both radial and axial loads of a disk drive. The bearing assembly includes a first clearance space between the shaft and the sleeve of the disk drive and includes a second clearance space between a thrust plate and the sleeve. Both of the clearance spaces are filled with a liquid lubricant to separate sliding metal surfaces. The two hydrodynamic bearings reduce non-repetitive runout, particle generation, and noise. Titcomb also describes hydrodynamic bearings in U.S. Pat. No. 5,516,212. Moreover, hydraulic bearings are described in U.S. Pat. Nos. 5,536,088 to Cheever et al. and 5,423,612 to Zang et al.
A third approach is to utilize aerodynamic bearings. In an article entitled, "Future Trends in Spindle Bearings for Disk Drives,"published within the November/December, 1995 volume of Data Storage, Kenneth A. Liebler describes a self-acting air bearing as an alternative to the use of roller and ball bearings within a disk drive. No specific structure is described and difficulties associated with air bearings are identified, but the article asserts that air bearing performance is almost invariable, due to the stable physical properties of air.
U.S. Pat. No. 5,358,339 to Konno et al. describes a disk drive that utilizes a hydrodynamic bearing to accommodate the radial load and employs a gas as a fluid for accommodating the axial load. That is, the fluid used for generating dynamic pressure in the thrust bearings is a gas, e.g. air, while the fluid used for generating dynamic pressure in the radial bearings is a lubricating liquid. A rotating sleeve functions as a bearing member for both the radial and the thrust bearings. The inside diameter of the rotating sleeve is a bearing member for the radial bearing, while the upper and lower planar surfaces of the sleeve function as bearing surfaces for the thrust bearing. The upper and lower surfaces face planar surfaces of thrust plates. The surfaces must be precisely machined in order to minimize turbulence during operation of the disk drive.
While the prior art assemblies operate well for their intended purpose, the performances of many of the devices may be further improved. For other devices, the cost may be significantly reduced.
What is needed is a low-cost, high-performance approach to providing bearings for a disk drive assembly.